Battery powered devices, such as cellular telephones and portable computers, for example, have gained appreciable market acceptance. Such devices offer portability and convenience to users, and many users have come to rely on them. The utility of portable devices is affected by the energy storage capacity of their associated battery pack. Conventional battery systems for portable devices are centered around nickel cadmium (NiCd) and nickel metal-hydride (NiMH) battery technologies, which are referred to collectively as nickel systems. Nickel systems provide robust batteries, and a great many accessories have been produced for them including chargers.
More recently, another battery system, lithium ion (Li-ion) has been brought to the marketplace. It offers significantly more energy storage capacity than nickel system batteries for a given weight, making it a very attractive alternative. Since most devices typically outlive the useful life of their associated batteries, it would be desirable to package Li-ion battery cells in a form so that existing portable products can take advantage of the increased energy storage offered by Li-ion. However, Li-ion is not recharged in the same manner as nickel system batteries.
Nickel system batteries are charged by applying a constant current at a predetermined rate, and monitoring at least one battery parameter until the parameter(s) indicates that the nickel system battery is near fully charged. An example of this would be to monitor battery temperature until the rate of temperature rise reaches a level indicative of a fully charged battery. A great many chargers have been sold into the market place that use this charge regime.
Li-ion, conversely, requires a somewhat different charge regime. It is charged by a constant current followed by a constant voltage charge regime. The voltage regulation of the constant voltage portion must be very precise. If the voltage is too low, the battery cells may not develop sufficient capacity. If the voltage is too high, the battery cell may become damaged. Since nickel system chargers are not typically designed to provide a constant voltage charge, Li-ion batteries are not easily retrofittable into existing nickel system chargers. By use of sophisticated electronics, it is possible to produce a retrofittable Li-ion battery, but the additional cost may be prohibitive to certain portions of the market. Some consumers may be more inclined to purchase chargers designed for Li-ion battery charging for use with a Li-ion battery that fits on an existing device.
Therefore there exists a need whereby a battery, such as a Li-ion battery, can be packaged so that a device can use the battery, and the battery has a means to lockout charging by an incompatible charger, and allow charging by a compatible charger. By incompatible it is meant that the charger, while able to receive the battery in a physical sense, is not designed to provide a compatible charge regime.